1. Field of the Invention
This invention relates generally to wheelchairs and more particularly to wheelchairs including a multiple speed, shiftable hub with a drive ring for selectively changing the gear ratio between the wheel and the drive ring.
2. Description of the Prior Art
Standard manual wheelchairs typically include large back wheels, sometimes fitted with a hand rim, wherein the user grasps the wheel or rim and applies a forward force to cause forward rotational movement of the wheels. This results in a constant 1:1 drive ratio which can cause difficulty for the user when encountering an incline or other difficult terrain. In addition, users in a reduced strength condition often have difficulty in using any wheelchair utilizing a 1:1 drive ratio. In many such cases, the only recourse is to use a powered wheelchair.
Over the years, several attempts have been made to develop a manual wheelchair where the ratio between the drive force and the wheels may be varied. Examples of such devices are illustrated in the Sasse U.S. Pat. No. 3,563,568; Zach U.S. Pat. No. 4,272,965; and the Seol U.S. Pat. No. 4,762,332.
In Sasse, the drive mechanism includes a pair of concentric driving and driven members with intervening gear trains therebetween. A shift lever is provided for operating the gear train. The drive member is a wheel disposed outwardly of and concentric with the standard wheel on the wheelchair. Sasse does not provide for any coasting or braking action and the user must remove one of his hands from the wheel in order to shift gears. This makes shifting while in motion difficult, particularly since each side of the wheelchair is controlled by a separate shift lever.
Seol provides a propulsion device incorporating a flywheel which is used with a lever, whereby the user grasps the lever on either side of the wheelchair and, in a rowing-like motion, transmits a force to the flywheel. The flywheel force is then transferred to the wheels to propel the chair forward. The user must remove his hands from the flywheel levers in order to change gears. Further, this device makes impractical any standard use of the chair where a direct rotational force is applied to the wheels.
Zach provides for a geared hub having at least one forward speed and an active hub brake. In Zach, the user is required to pull a shift chain on each side of the wheelchair to effect a gear change. Again, the user must remove both hands from the wheels to change gears.
None of the prior art wheelchairs provides for a drive ring which engages the standard wheel when moved in a forward direction, while providing for hands-on gear shifting, coasting, and/or braking action. The present invention overcomes these and other disadvantages while providing a safe and simple to use configuration.